Aneurysms occur in blood vessels in locations where, due to age, disease or genetic predisposition, the blood vessel strength or resiliency is insufficient to enable the blood vessel wall to retain its shape as blood flows therethrough, resulting in a ballooning or stretching of the blood vessel at the limited strength/resiliency location to thereby form an aneurysmal sac. If the aneurysm is left untreated, the blood vessel wall may continue to expand, to the point where the remaining strength of the blood vessel wall is below that necessary to prevent rupture, and the blood vessel will fail at the aneurysm location, often with fatal result.
To prevent rupture, a stent graft of a tubular construction may be introduced into the blood vessel, for example intraluminally. Typically, the stent graft is deployed and secured in a location within the blood vessel such that the stent graft spans the aneurysmal sac. The outer surface of the stent graft, at its opposed ends, is sealed to the interior wall of the blood vessel at a location where the blood vessel wall has not suffered a loss of strength or resiliency. Blood flow in the vessel is thus channeled through the hollow interior of the stent graft, thereby reducing, if not eliminating, any stress on the blood vessel wall at the aneurysmal sac location. Therefore, the risk of rupture of the blood vessel wall at the aneurysmal location is significantly reduced, if not eliminated, and blood can continue to flow through to the downstream blood vessels without interruption.
In many cases, however, the damaged or defected portion of the vasculature may include a branch vessel. For example, in the case of the abdominal aorta, there are at least three branch vessels, including the celiac, mesenteric, and renal arteries, leading to various other body organs. Thus, when the damaged portion of the vessel includes one or more of these branch vessels, some accommodation must be made to ensure that the stent graft does not block or hinder blood flow through the branch vessel.
A common method to provide continued blood flow to branch vessels includes by-pass vessels surgically located in an undamaged region of the aorta that is not stented. Such invasive methods, however, are undesirable. A less invasive technique to provide continued blood flow to branch vessels includes the placement of holes or fenestrations in the stent graft that are aligned with the side branch vessel so as to allow blood to continue to flow into the side branch vessel. This approach is the preferred method since it does not involve major vascular surgery.